Problem: Which of these numbers is composite? ${7,\ 11,\ 29,\ 43,\ 45}$
Explanation: A composite number is a number that has more than two factors (including 1 and itself). 7, 11, 29, and 43 each have only two factors. The factors of 45 are 1, 3, 5, 9, 15, and 45. Thus, 45 is the composite number.